NORRISTOWN, Pa. — Jurors in the Bill Cosby trial heard from the first witness Monday — a woman who testified in tears that she was drugged and sexually assaulted by the comedian in 1996 and who then came under a blistering cross-examination from the defense.

“Did anyone tell you to get selective amnesia in this case?” Cosby attorney Brian McMonagle screeched at the woman, who had worked for Cosby’s agent at the William Morris Agency.

He questioned why she had waited for almost 20 years to come forward and publicly accuse Cosby at a January 2015 press conference as allegations of sexual misconduct by dozens of other women piled up.

“I was very afraid because I have a secret about the biggest celebrity in the world at that time and it was just me, just me and my word against his,” she shot back from the witness stand.

It was a dramatic beginning to the trial of the world-famous comedian, who listened intently as the legal fireworks erupted inside the Montgomery County Courthouse.

Cosby, 79, is not charged with attacking the first witness, who is described in court documents as Prior Alleged Victim No. 6, but has used the pseudonym Kacey in public appearances.

Prosecutors put her on the stand in the hopes of proving a pattern of behavior by the star, who is on trial for allegedly drugging and molesting another woman, Andrea Constand, in 2004.

She began her afternoon testimony in a clear and calm voice.

She said that Cosby took an interest in her while she was working as an assistant to his late agent, Tom Illius, at the William Morris Agency, in Los Angeles the 1990s — in a “fatherly, favorite uncle, Dr. Huxtable kind of way.”

Bill Cosby arrives with actress Keshia Knight Pulliam at the Montgomery County Courthouse before the opening of the sexual assault trail June 5, 2017 in Norristown, Pennsylvania.Mark Makela / Getty Images

Cosby would call often and he invited her and her family to shows and gave her a giant Bird of Paradise plant for her birthday. She was flattered, she said, because he was such a big star, the most important client of the agency.

But, she said, there were interactions that made her uncomfortable. He would call her to chat and tell her to keep it from Illius. He invited her to her house to teach her about TV production, and had her rehearse a scene that would have required her to kiss him, which she “couldn’t do.”

In 1996, she said, he invited her to his bungalow at the Bel-Air Hotel for lunch and to discuss her career. He met her in robe and slippers and repeatedly urged her to take a pill to relax.

“I pretended to swallow it with water and he handed me a glass of wine and he leaned forward and said open your mouth lift up your tongue and I did and there it was under my tongue,” she said, choking up frequently during this portion of the testimony.

She said she ultimately swallowed the pill and then locked herself in the bathroom to compose herself. The sink was covered with pill bottles, but she was having trouble reading the labels. Before long, she said, she felt like she was “under water” and then her memory went blank.

“I sort of came to in the bedroom of the bungalow … on the bed,” she said.

Her dress was half-off and her breasts were exposed and Cosby was on the bed, behind her, she said.

“I remember hearing grunting sounds behind me,” she said, going on to say that he put lotion on her hand and had her masturbate him.

The witness grabbed a tissue and blotted her eyes and then continued testifying, saying she did not remember how she got home.

She said when she went back to work, she eavesdropped on a phone call from Cosby to Illius in which the star described her as a “problem,” she said.

Attorney Gloria Allred arrives at the Montgomery County Courthouse before the opening of the sexual assault trail of Bill Cosby June 5, 2017 in Norristown, Pennsylvania.Mark Makela / Getty Images

By her account, she went to human resources, fearing she was about to be fired, but did not go into detail about what happened at the Bel-Air hotel. “I was a little bit of a mess,” she said.

She was sent home and never returned to work, she said. Instead, she contacted an attorney who advised her not to take action, and she filed a worker’s compensation claim.

During a deposition for the worker’s compensation case, she said, she described what had happened at the hotel.

“It was one of the most humiliating, embarrassing things I’ve ever had to do,” she said tearfully.

When it was McMonagle’s turn, he went on the offensive immediately, attacking her memory and credibility with rapid-fire questions, his voice rising as he pressed her for answers.

The witness frequently responded that she could not recall certain details but did not backtrack from the timeline she gave the jurors — seven men and five women — about her encounters with Cosby.led her about why the account she gave from the stand did not match up with what he said were lawyer’s notes from a deposition in the 1996 worker’s compensation case.

At that time, he claimed, she testified that she visited Cosby at the Bel-Air hotel in 1990 and that the meeting where she acted out a scene was in 1996. She said she didn’t recall the deposition and was “bawling” throughout it, mortified at having to talk about the hotel incident.

He suggested her high-profile attorney, Gloria Allred — who represents a raft of Cosby accusers and was watching from the first row in court — had coached her. She denied it.

He intimated that she had an affair with Cosby and that Cosby had given her money — $100 to get her hair done and $400 for a doctor appointment for her grandmother. She said he had not.

He even grilled her on whether she had done drugs with a former boyfriend, a well-known singer.

“Isn’t it a fact that you were doing drugs in the 1990s?” McMonagle pressed her.

“I would say no,” she responded.

No. 6 was called to the stand after a morning devoted to opening arguments in which a prosecutor portrayed Cosby as a man who used fame and drugs to sexually assault women and his lawyer painted Constand as a liar.

“Trust. Betrayal. And an inability to consent. That’s what this case is about, ladies and gentlemen,” Montgomery County Assistant District Attorney Kristen Feden told the Pennsylvania jury, her voice dripping with contempt at times.

“This is a case about a man — this man — who used his power and his fame and his previously practiced method of placing a young trusting woman in an incapacitated state so he could sexually pleasure herself, so she couldn’t say no,” Feden said.

Feden told jurors that the defense would attack Constand for continuing to have contact with Cosby after the incident and for waiting for so long to make a report. Those issues, she said, were “distractions.”

In a theatrical opening, McMonagle went after the prosecutor’s characterization.

“The false accusation of sexual assault is an attack on human innocence,” he said. “It’s not a distraction!”

He pointed out inconsistencies in Constand’s various statements, including an early claim that before the alleged attack she had never been alone with him and that she did not have contact with him afterward.

Wielding phone records, he said, “After the so-called paralyzation and drugging and assault, there were 72 phone calls. She called him 53 times.”

The trial is expected to last two weeks. Cosby is charged with three counts of aggravated indecent assault, which carries a maximum of 10 years in prison.

When he arrived at the courthouse Monday, he was met by actress Keshia Knight Pulliam, who played his youngest daughter on “The Cosby Show.”

“It’s easy to support when things are good,” Pulliam told reporters. “But true family is who shows up when things aren’t good.

“It’s the jury’s job to decide guilt or innocence. It’s not mine or anyone else’s,” she added.